Orthogonal Frequency Division Multiplexing (OFDM) systems generally include a cyclic extension (or guard interval) with each transmitted OFDM symbol. The cyclic extension is intended to eliminate inter-symbol and inter-carrier interference in delay spread channels. However, if the channel impulse response is longer than the cyclic extension, the portion of the impulse response that is outside the extension causes self-interference.
Delay spread detection circuits exist in the art to estimate the delay spread in a radio frequency signal. Most of the existing delay spread sensors are designed for single-carrier systems. For example, a prior art delay spread estimator disclosed in U.S. Pat. No. 5,602,484 A1 detects the presence of an excess delay spread after estimating the channel by an implementation of a matched filter operation. Another prior art delay spread estimator disclosed in U.S. Pat. No. 6,028,901 A1 implements a matched filter operation to estimate the channel and extract the channel's impulse response. However, for multi-carrier systems, a process of channel estimation as proposed by the art is computationally intensive, because it involves a fast Fourier transform (“FFT”) followed by an inverse fast Fourier transform (“IFFT”) to extract the channel impulse response.
The present invention advances the art by a contribution of a method and a receiver for detecting the presence of an excess delay spread in communication systems.